EP-A-2243992 discloses a high pressure pipe coupling construction, comprising at least one high pressure pipe as well as a coupling connected to a pipe end of said pipe, said pipe having a pipe wall which comprises a reinforcement layer of helically wound fibers embedded in a matrix material, said coupling comprising at least one metal outer sleeve crimped onto the outer surface of the pipe end and an inner sleeve sealed with respect to the inner surface of the pipe end and overlapping the outer sleeve in axial direction. The metal outer sleeve protrudes in axial direction with respect to the inner sleeve by means of a protruding outer sleeve part which at least partly is clamped onto the outer surface of the pipe.
The pipe of this prior art pipe coupling comprises fibers and matrix materials which are chemically inert with respect to the aggressive components of crude oil and gas. The helically wound character of the fibers furthermore provides a high mechanical strength and stiffness for coping with high internal pressures in a pipeline. Moreover, the relatively long outer sleeve of this prior art coupling favorable influences the mechanical connection and force transfer between the pipe and the coupling, by making use of the so-called capstan effect.
This capstan effect results from the helical path of the fibers or threads within the outer sleeve. This provides a so-called encirclement of the fibers or threads within the outer sleeve. The ends of the fibers are held against sliding or slipping displacements within the pipe wall material. The fibers may be arranged in several fashions. According to a first possibility, the fibers are arranged parallel to each other in the form of a tape. The tape comprises furthermore a plastic matrix material, and is wound helically within the pipe wall. By melting together the plastic material of the tapes and of the coating layer, the fibers are held reliably against slipping with respect to the plastic material. Preferably, several tapes are wound on top of each other with opposite winding angles. The number of tapes in one winding direction is preferably the same as the number of tapes in the opposite winding direction so as to balance the forces in the tapes. Small woven fibre/cord tapes or parallel fibre/cord tapes are braided or wound onto the pipe. The fibre may be applied as woven or parallel tapes. According to a second possibility, relatively narrow tapes are woven into each other. In this embodiment as well, the tapes are wound with opposite winding angles. The fibers may be applied in a braided or knitted fashion within the tapes.
The pipe end itself is fixed by compression of the pipe wall between the outer sleeve and the inner sleeve. As soon as these fibers or threads are subjected to tensile forces as a result of pressures in the pipe, the fibers or threads develop increasing friction forces with respect to the inner surface of the outer sleeve, comparable to the friction forces which develop in a cable which is slung around a capstan. For this holding phenomenon to become effective, it is sufficient to merely prevent the cable from slipping with respect to the capstan, which requires only a low to moderate holding force to be exerted on the free end of the cable. As a result of the capstan effect, a relatively high holding force is obtained in the cable. Similarly, the fibers or threads respectively the strands containing these fibers or threads of the pipe only need to be slightly clamped by exerting a low or moderate clamping force on the ends thereof, for obtaining a relatively high holding force of the pipe end with respect to the outer sleeve.